The present invention is generally directed to an apparatus for controlling an appliance, the appliance including a compressor, a fan, and a heater. More particularly, the preferred embodiment of the present invention is directed to a defrost controller for selectively completing a circuit from an energy source through at least one of a heater, a fan, and a compressor.
Appliances such as refrigerators and freezers generally operate in one of a plurality of operating modes. Such devices generally include a compressor coupled with an evaporator for cooling air, a fan for circulating cool air throughout the device, and a defrost heater for defrosting the coils of the evaporator. A control circuit selectively couples one or more of these components to an energy source such as a power supply to operate in one of the plurality of operating modes.
In a first operating mode, the compressor and the fan are coupled to the energy source and operate to cool the air in the appliance and circulate the cool air throughout the device. In a second operating mode, the defrost heater is coupled to the energy source and operates to defrost the evaporator when a predetermined frost load has accumulated on the evaporator. For maximizing efficient utilization of energy, the cooling mode and the defrost mode of operation are mutually exclusive. It is inefficient to try to cool air in the appliance and defrost at the same time.
A third operating mode is drip time. For a predetermined time after the defrost heater is deenergized, but before the compressor is energized, each of the defrost heater, the compressor, and the fan are decoupled from the energy source to allow moisture to drip from the evaporator coils. Drip time may be approximately two minutes in duration. Removal of moisture from the evaporator coils reduces ice formation on the coils during a subsequent cooling cycle. Ice on the evaporator coils insulates the coils and renders heat exchanging less efficient during cooling cycles. It is for the very purpose of removing such ice buildup that defrosting is effected.
A fourth operating mode, fan delay, preferably follows the drip time operating mode. During fan delay, only the compressor is coupled to the energy source. This allows air around the evaporator coils to cool prior to coupling the fan to the energy source to circulate the cool air. Fan delay improves performance of the appliance by permitting only the circulation of cool air, and not air which has been warmed during the defrost cycle. Fan delay time may be ten to fifteen minutes in duration.
Following the fan delay, the fan, along with the compressor, is coupled with the energy source and the cooling operating mode (first operating mode) begins. Under control of the control circuit, the appliance cycles repetitively among the four operating modes.
Prior art defrost controllers are not well adapted to providing all four modes of operation. Prior art defrost controllers include a single control output for controlling a single relay. The single pole, dual throw relay selects between a compressor run mode for cooling or a defrost mode. Fan delay and drip time modes are controlled through external devices or are not available.
Prior art defrost controller circuits include a circuit for energizing and deenergizing the relay coil of the relay used for mode selection. The defrost controller provides a current to the relay coil to energize the relay coil to select one of the cooling mode or the defrost mode. The defrost controller removes the current from the relay coil to deenergize the relay coil and select the other of the cooling mode or defrost mode.
Some defrost controller circuits control more than a single relay. These defrost controllers have high part counts and use considerable electrical energy to control more than one relay. Prior art relay control circuits generally provide a single current path for energizing the relay coil of each relay to be controlled. Prior art appliance controllers have lacked a way to control multiple relays in an appliance using a single current path.
The present invention overcomes these limitations and provides other advantages over the prior art. The present invention provides an apparatus which readily couples a compressor, a fan, and a heater to an energy source to provide positive operational control of the apparatus in any one of a plurality of operating modes, such as the four operating modes described above.